1. Field of the Invention:
The present invention relates to a disk recording and reproducing apparatus employed in electronic computers and word processors for recording information in a disk and reproducing the recorded information and, more specifically, to a disk clamping device for such a disk recording and reproducing apparatus, for clamping and rotating a disk.
2. Description of the Prior Art:
A conventional disk clamping device is shown in FIG. 2. The constitution of the disk clamping device will be described with reference to FIG. 2.
A spindle 2 to be driven by a motor, not shown, is supported in bearings 3 on a housing 1. A wheel 4 is fixed to the upper end of the spindle 2. A circular recess 4a is formed in the central portion of the wheel 4 coaxially with the spindle 2. The diameter of the circular recess 4a is substantially the same as the diameter of a central hole, not shown, of a flexible disk 5 to be placed on the upper surface 4b of the wheel 4. A frame 6 is swingable in a vertical plane toward and away from the wheel 4. A hole 6a is formed in the frame 6. An arbor 7 having a diameter smaller than that of the hole 6a is received loosely in the hole 6a so as to be radially movable in the hole 6a. A stopper 8 fitted on the upper end of the arbor 7 is seated on the upper surface of the frame 6 with a washer 9 therebetween to retain the arbor 7 in place on the frame 6. A hub 11 is supported on a bearing 10 on the arbor 7 at the lower end of the same.
The hub 11 is formed by molding a synthetic resin in a unitary construction. A central hole 12 is formed in the boss of the hub 11. The bearing 10 is fitted in forced fit in the central bore 12 and is seated on the upper surface of an annular protrusion 13 formed in the inner surface of the central bore 12 in the lower part of the same. The arbor 7 is connected to the hub 11 with the upper surface of a flange 7a formed at the lower end thereof, in contact with the lower surface of the annular protrusion 13. Radial arms 14 are formed in the peripheral portion of a flange formed at the upper end of the boss of the hub 11. The outer end of each arm 14 is bent downward and is joined to a pressing part 15. A pressing surface 15a is formed in the lower surface of the pressing part 15. A plurality of pairs of flexible disk guides 16 having a comparatively small wall thickness are formed at regular angular intervals so as to depend from the pressing parts 15. Each disk guide 16 has a vertical positioning wall 17 projecting vertically and downward from the pressing part 15 and an inclined guide wall 18 extending inward from the lower end of the positioning wall 17. FIG. 6 is a detail view of the radial arm 14 and the associated parts of the hub 11. The pressing parts 15 and the positioning walls 17 are arranged alternately, and hence the angular position of the pressing parts 15 is different from that of the positioning walls 17. The diameter D.sub.1 of a circular cylinder containing the respective outer surfaces of the positioning walls 17 is slightly greater than the diameter D.sub.2 of the circular recess 4a of the wheel 4. Accordingly, when the hub 11 is fitted in the recess 4a of the wheel 4, the disk guides 16 are elastically deformed so that the positioning walls 17 of the disk guides 16 are in close contact with the inner surface of the circular recess 4a . A compression coil spring 19 is interposed between the bearing 10 fixedly fitted in the bore 12 of the hub 11 and the inner surface of the frame 6.
The manner of operation of this conventional disk clamping device will be described hereinafter.
In the initial state, the frame 6 is raised to an upper position by a spring, not shown, as illustrated in FIG. 2. The hub 11 is pressed at the annular protrusion 13 formed in the bore 12 against the flange 7a of the arbor 7 by the compression coil spring 19.
After the disk 5 has been inserted through the disk inlet, not shown, of the disk recording and reproducing apparatus into the disk recording and reproducing apparatus as far as the central hole of the disk 5 is located above the circular recess 4a of the wheel 4, the frame 6 is turned downward manually or by suitable means in a direction indicated by an arrow A to move the hub 11 toward the wheel 4. Then, first the lower ends of the guiding walls 18 of the hub 11 enter the circular recess 4a of the wheel 4 through the central hole of the disk 5. While the guiding walls 18 of the hub 11 move into the circular recess 4a of the wheel 4, the guiding walls 18 engage the boundary of the central hole of the disk 5 to move the disk 5 in a radial direction. When the arbor 7 is dislocated from the correct position corresponding to the spindle 2, the arbor 7 is brought into alignment with the spindle 2 through the engagement of the guiding walls 18 and the inner circumference of the wheel 4. Thus, the disk 5 is moved laterally by the guiding walls 18 of the hub 11 as the hub 11 is lowered toward the wheel 4 so that the center thereof approaches the center axis of the spindle 2 gradually for temporary alignment. Since the diameter D.sub.1 of the positioning walls 17 is slightly greater than the diameter D.sub.2 of the circular recess 4a of the wheel 4, the positioning walls 17 are bent elastically by the inner circumference of the wheel 4 when the positioning walls 17 enter the circular recess 4a, while the disk 5 is brought into alignment with the circular recess 4a by the positioning walls 17. Thus, the disk 5 is positioned correctly on the wheel 4. As the hub 11 is lowered further, the pressing surfaces 15a of the pressing parts 15 press the disk 5 against the upper surface 4b of the wheel 4, and then the downward movement of the hub 11 is stopped temporarily. Then, the hub 11 is lowered further compressing the compression coil spring 19, whereby the pressing parts 15 apply the pressure of the compression coil spring transmitted thereto through the radial arms 14 to the disk 5 to secure the disk 5 on the upper surface 4b of the wheel 4. Uppon the arrival of the frame 6 at the lowermost position, the frame 6 is stopped to complete the disk centering and clamping operation.
After the downward movement of the frame 6 has been stopped, the spindle 2 is driven to rotate the disk 5 and a magnetic head, not shown, disposed opposite to the recording surface of the disk 5 write information in the disk 5 or read the information recorded in the disk 5 from the disk 5.
In discharging the disk 5 outside the disk recording and reproducing apparatus, the frame 6 is turned upward, and then the hub 11 is restored to the initial position by the resilience of the compression coil spring 19.
However, this conventional disk clamping mechanism has the following drawbacks. Since the pressing parts 15 and the disk guides 16 of the hub 11 are arranged alternately at angular intervals, the point of action of a reaction force exerted by the wheel 4 on each positioning wall 17 and the point of action of a reaction force exerted by the wheel 4 on the adjacent pressing part 15 are not on the same radial line when the hub 11 engage the wheel 4 firmly, and hence the reaction force exerted on the pressing parts 15 and the reaction force exerted on the disk guides 16 tend to twist the radial arms 14. Consequently, the disk 5 held between the pressing surfaces 15a of the hub 11 and the upper surface 4b of the wheel 4 tends to slip relative to the wheel 4 when the wheel 4 is rotated, and hence the disk 5 is unable to be rotated at a predetermined revolving rate. Therefore, correct writing or reading of information is impossible and the disk 5 is liable to be damaged when the same is clamped unsteadily and rotated irregularly.